Wireless full duplex refers to a technology that a wireless transceiver implements simultaneous receiving and sending. In designing of a conventional transceiver in a wireless network, to implement full duplex, either it is required to use two independent channels to separately perform sending and receiving, or it is required to use a time division system to separate timeslots for receiving and sending. In both of the two technologies, a wireless spectrum is not used effectively. In a case in which same bandwidth is occupied, the two full-duplex technologies fail to improve transmission efficiency of an entire communications system essentially.
A biggest problem in implementing full duplex at a same time and at a same frequency lies in that, when each of transmit antennas of two parties simultaneously sends a signal to a receive antenna of the other party, the sent signal is not only received by the receive antenna of the other party but also received by a receive antenna of the own party. Moreover, a distance from the receive antenna of the own party to the transmit antenna of the own party is much shorter than a distance from the receive antenna of the own party to a transmit antenna of the other party, and the signal fades in a transmission process. Therefore, the signal received by the receive antenna of the own party and sent by the transmit antenna of the own party is much stronger than the signal received by the receive antenna of the own party and sent by the transmit antenna of the other party, thereby submerging the signal sent by the transmit antenna of the other party.
Referring to FIG. 1, to improve utilization of the wireless spectrum, the prior art provides a full-duplex antenna, which can perform full-duplex transmission at a same frequency and in a same timeslot without affecting a signal-to-noise ratio of a receive signal of the full-duplex antenna. The full-duplex antenna includes a first transmit antenna 111, a receive antenna 113, and a second transmit antenna 115. All of the first transmit antenna 111, the receive antenna 113, and the second transmit antenna 115 are omnidirectional antennas. The first transmit antenna 111 is disposed on one side of the receive antenna 113, and the second transmit antenna 115 is disposed on the other side of the receive antenna 113. Moreover, a distance between the first transmit antenna 111 and the receive antenna 113 is d, and a distance between the second transmit antenna 115 and the receive antenna 113 is d+λ/2, where λ represents a wavelength.
Referring to FIG. 2, the full-duplex antenna provided in the prior art is applied to each of a first communication party 210 and a second communication party 220. The first communication party 210 is provided with a first transmit antenna 211, a first receive antenna 213, and a second transmit antenna 215. The second communication party 220 is provided with a third transmit antenna 221, a second receive antenna 223, and a fourth transmit antenna 225.
On one hand, the first communication party 210 needs to send data to the second communication party 220, and therefore, the first transmit antenna 211 and the second transmit antenna 215 simultaneously send a same signal to the external. Moreover, both of the signals sent by the first transmit antenna 211 and the second transmit antenna 215 are simultaneously sent to the first receive antenna 213 and the second receive antenna 223. However, the first receive antenna 213 is not desired to receive the signals sent by the first transmit antenna 211 and the second transmit antenna 215. Moreover, distances between the first receive antenna 213 and the first transmit antenna 211 and between the first receive antenna 213 and the second transmit antenna 215 are much shorter than distances between the second receive antenna 223 and the first transmit antenna 211 and between the second receive antenna 223 and the second transmit antenna 215.
Therefore, if the signals sent by the first transmit antenna 211 and the second transmit antenna 215 are received by the first receive antenna 213, strong interference is caused to the first receive antenna 213. However, a distance between the first transmit antenna 211 and the first receive antenna 213 is d, and a distance between the second transmit antenna 215 and the first receive antenna 213 is d+λ/2, that is, the two distances differ by a half of a wavelength. Therefore, the signal sent by the first transmit antenna 211 to the first receive antenna 213 and the signal sent by the second transmit antenna 215 to the first receive antenna 213 are exactly the same in signal strength and reverse in phase, and are mutually canceled. Therefore, the signals sent by the first transmit antenna 211 and the second transmit antenna 215 do not cause strong interference to the first receive antenna 213. The signals sent by the first transmit antenna 211 and the second transmit antenna 215 are reflected and refracted multiple times in space transmission, and transmitted to the second receive antenna 223 through multiple paths (a multipath effect), and are received by the second receive antenna 223.
On the other hand, the second communication party 220 needs to send data to the first communication party 210, and therefore, the third transmit antenna 221 and the fourth transmit antenna 225 simultaneously send a same signal to the external. Moreover, both of the signals sent by the third transmit antenna 221 and the fourth transmit antenna 225 are simultaneously sent to the second receive antenna 223 and the first receive antenna 213. However, the second receive antenna 223 is not desired to receive the signals sent by the third transmit antenna 221 and the fourth transmit antenna 225. Moreover, distances between the second receive antenna 223 and the third transmit antenna 221 and between the second receive antenna 223 and the fourth transmit antenna 225 are much shorter than distances between the first receive antenna 213 and the third transmit antenna 221 and between the first receive antenna 213 and the fourth transmit antenna 225. Therefore, if the signals sent by the third transmit antenna 221 and the fourth transmit antenna 225 are received by the second receive antenna 223, strong interference is caused to the second receive antenna 223.
However, a distance between the third transmit antenna 221 and the second receive antenna 223 is d, and a distance between the fourth transmit antenna 225 and the second receive antenna 223 is d+λ/2. Therefore, the signal sent by the third transmit antenna 221 to the second receive antenna 223 and the signal sent by the fourth transmit antenna 225 to the second receive antenna 223 are exactly the same in signal strength and reverse in phase, and are mutually canceled. Therefore, the signals sent by the third transmit antenna 221 and the fourth transmit antenna 225 do not cause strong interference to the second receive antenna 223. The signals sent by the third transmit antenna 221 and the fourth transmit antenna 225 are reflected and refracted multiple times in space transmission, and transmitted to the first receive antenna 213 through multiple paths (the multipath effect), and are received by the first receive antenna 213.
The first transmit antenna 211 and the second transmit antenna 215 of the first communication party 210 do not affect the first receive antenna 213, and the third transmit antenna 221 and the fourth transmit antenna 225 of the second communication party 220 do not affect the second receive antenna 223. Therefore, the first communication party 210 and the second communication party 220 can perform bidirectional data transmission at a same time and at a same frequency.
However, in this manner, when the distance between the first transmit antenna 111 and the receive antenna 113 is d, the distance between the second transmit antenna 115 and the receive antenna 113 must be d+λ/2. Therefore, when a used wavelength changes, the distance between the second transmit antenna 115 and the receive antenna 113 must change. Moreover, a wideband signal includes multiple frequencies, and wavelengths corresponding to the frequencies are all different. However, the distance between the second transmit antenna 115 and the receive antenna 113 can be set according to only one of the wavelengths. Therefore, the manner cannot be applied to the wideband signal.